Android6.0 camera个数探测

近期在排查打开相机黑屏的问题，然后就跟了一下android camera的框架。根据log分析发现是camera个数为0，然后就进行代码流程跟踪。由于开发平台是mtk平台，log提示上层报错的对应代码逻辑如下图。

mCameraService是ICameraService接口类型。

获取服务的名称如下：

并且是通过aidl跟底层c++通信。
frameworks/base/core/java/android/hardware/ICameraService.aidl

/** Copyright (C) 2013 The Android Open Source Project** Licensed under the Apache License, Version 2.0 (the "License");* you may not use this file except in compliance with the License.* You may obtain a copy of the License at**      http://www.apache.org/licenses/LICENSE-2.0** Unless required by applicable law or agreed to in writing, software* distributed under the License is distributed on an "AS IS" BASIS,* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.* See the License for the specific language governing permissions and* limitations under the License.*/package android.hardware;import android.hardware.ICamera;
import android.hardware.ICameraClient;
import android.hardware.camera2.ICameraDeviceUser;
import android.hardware.camera2.ICameraDeviceCallbacks;
import android.hardware.camera2.impl.CameraMetadataNative;
import android.hardware.camera2.utils.BinderHolder;
import android.hardware.ICameraServiceListener;
import android.hardware.CameraInfo;/*** Binder interface for the native camera service running in mediaserver.** @hide*/
interface ICameraService
{/*** Keep up-to-date with frameworks/av/include/camera/ICameraService.h*/int getNumberOfCameras(int type);// rest of 'int' return values in this file are actually status_tint getCameraInfo(int cameraId, out CameraInfo info);int connect(ICameraClient client, int cameraId,String opPackageName,int clientUid,// Container for an ICamera objectout BinderHolder device);int connectDevice(ICameraDeviceCallbacks callbacks, int cameraId,String opPackageName,int clientUid,// Container for an ICameraDeviceUser objectout BinderHolder device);int addListener(ICameraServiceListener listener);int removeListener(ICameraServiceListener listener);int getCameraCharacteristics(int cameraId, out CameraMetadataNative info);/*** The java stubs for this method are not intended to be used.  Please use* the native stub in frameworks/av/include/camera/ICameraService.h instead.* The BinderHolder output is being used as a placeholder, and will not be* well-formatted in the generated java method.*/int getCameraVendorTagDescriptor(out BinderHolder desc);// Writes the camera1 parameters into a single-element array.int getLegacyParameters(int cameraId, out String[] parameters);// Determines if a particular API version is supported; see ICameraService.h for version definesint supportsCameraApi(int cameraId, int apiVersion);int connectLegacy(ICameraClient client, int cameraId,int halVersion,String opPackageName,int clientUid,// Container for an ICamera objectout BinderHolder device);int setTorchMode(String CameraId, boolean enabled, IBinder clientBinder);/*** Notify the camera service of a system event.  Should only be called from system_server.** Callers require the android.permission.CAMERA_SEND_SYSTEM_EVENTS permission.*/oneway void notifySystemEvent(int eventId, in int[] args);// atc aosp enhancement: cvbs camera , cvbs format detect.int atcSetCameraInfoUpdateFlag(int flag);}

当时我们公司的应用开发工程师打开相机时会进行摄像头探测，通过调用framework的aidl接口去调用mCameraService.getNumberOfCameras()探测camera个数，总的流程会通过三部分讲解。分别为framework层，native层，driver层三部分。

一：framework层

注意：CarmerServiceDetector中的mCameraService是直接通过aidl调用到c++的ＣameraSevice服务的。具体代码如下：

private static final String CAMERA_SERVICE_BINDER_NAME = "media.camera";
......//代表中间有很多代码
mCameraService = ICameraService.Stub.asInterface(ServiceManager.getService(CAMERA_SERVICE_BINDER_NAME));

我们看下ＣameraSevice.cpp是如何启动注册服务以及完成ICameraService.aidl的接口调用的。

//代码路径：frameworks/av/media/mediaserver/main_mediaserver.cpp
int main(int argc __unused, char** argv)
{......//代表中间走过了很多代码//相机服务开始初始化并注册CameraService::instantiate();.....ProcessState::self()->startThreadPool();IPCThreadState::self()->joinThreadPool();}
}

class CameraService :public BinderService<CameraService>,public BnCameraService,public IBinder::DeathRecipient,public camera_module_callbacks_t
{friend class BinderService<CameraService>;
public:class Client;class BasicClient;......// 获取注册服务的名字，提供上层aidl找到该服务static char const* getServiceName() { return "media.camera"; }.....
}

注意：在instantiate函数中，将CameraService注册到系统的binder service列表中，这样以后上层java就可以通过aid调到CameraService提供的方法了。并且我们可以通过注册CameraService时会调用getServiceName名字注册跟上层ServiceManager.getService(CAMERA_SERVICE_BINDER_NAME)时的名字都是media.camera可得知CameraService便正是上层通过aidl调用c++服务。

二：HAL层

经过上面的调用过程最终调用到mtk的carmer hal层，至于怎么调用到这里的，写过adroid hal层的都应该大概知道。

//path:vendor/mediatek/proprietary/hardware/mtkcam/legacy/module_hal/module/module.h
static
int
get_number_of_cameras(void)
{return  NSCam::getCamDeviceManager()->getNumberOfDevices();
}

//path:vendor/mediatek/proprietary/hardware/mtkcam/common/include/device/ICamDeviceManager.h
#ifndef _MTK_HARDWARE_INCLUDE_MTKCAM_DEVICE_ICAMDEVICEMANAGER_H_
#define _MTK_HARDWARE_INCLUDE_MTKCAM_DEVICE_ICAMDEVICEMANAGER_H_
//
#include <utils/Errors.h>
#include <utils/StrongPointer.h>
//
#include <hardware/camera_common.h>
#include <common.h>
.....
namespace NSCam {class ICamDevice;class ICamDeviceManager
{...
};
ICamDeviceManager*  getCamDeviceManager();//返回一个ICamDeviceManager类型对象
};  //namespace NSCam
#endif  //_MTK_HARDWARE_INCLUDE_MTKCAM_DEVICE_ICAMDEVICEMANAGER_H_

查看具体getCamDeviceManager实现，可知返回就只有返回CamDeviceManagerImp类型指针。

//path:vendor/mediatek/proprietary/hardware/mtkcam/legacy/platform/mt3561m/devicemgr/CamDeviceManagerImp.cpp
namespace
{CamDeviceManagerImp gCamDeviceManager;
}   //namespacenamespace NSCam {ICamDeviceManager*
getCamDeviceManager()
{return  &gCamDeviceManager;//返回CamDeviceManagerImp类型函数
}
}

CamDeviceManagerImp的声明，继承CamDeviceManagerBase

//path:vendor/mediatek/proprietary/hardware/mtkcam/legacy/platform/mt3561m/devicemgr/CamDeviceManagerImp.h
class CamDeviceManagerImp : public CamDeviceManagerBase
{public:                             Instantiation.CamDeviceManagerImp();protected:                          Operations.virtual android::status_t           validateOpenLocked(int32_t i4OpenId,uint32_t device_version) const;virtual int32_t                     enumDeviceLocked();virtual android::status_t           setTorchModeLocked(int const deviceId,bool enabled,bool notifyEvent);virtual android::status_t           setTorchAvailableLocked(int const deviceId,bool available);
};

从上面CamDeviceManagerImp的类看出，其并没有定义方法getNumberOfDevices，但是继承了CamDeviceManagerBase，所以很有可能getNumberOfDevices是getNumberOfDevices的方法。跟踪代码发现如下，果然如此。

//path:vendor/mediatek/proprietary/hardware/mtkcam/legacy/module_hal/devicemgr/CamDeviceManagerBase.cpp
int32_t
CamDeviceManagerBase::
getNumberOfDevices()
{RWLock::AutoWLock _l(mRWLock);//if  ( 0 != mi4DeviceNum ){MY_LOGD("#devices:%d", mi4DeviceNum);//返回支持摄像头个数。一般来说初始化过一次后就得到支持的camera个数了。}else{//第一次开机启动一般通过走这里去获取支持camera的数量Utils::CamProfile _profile(__FUNCTION__, "CamDeviceManagerBase");mi4DeviceNum = enumDeviceLocked();_profile.print("");}//return  mi4DeviceNum;
}

下面我们通过uml图来说明下调用流程：

最后camera hal层会通过ioctl去访问底层驱动，并且检测camera的sensor id是否有效，有效数目便是支持返回的camera个数。代码逻辑如下：

//path:vendor/mediatek/proprietary/hardware/mtkcam/legacy/platform/mt3561m/hal/sensor/imgsensor_drv.cpp
MINT32
ImgSensorDrv::impSearchSensor(pfExIdChk pExIdChkCbf)
{......for (i = 0; i < MAX_NUM_OF_SUPPORT_SENSOR; i++) {//end of driver listif (m_pstSensorInitFunc[i].getCameraDefault == NULL) {LOG_MSG("m_pstSensorInitFunc[i].getCameraDefault is NULL: %d \n", i);break;}//set sensor driverid[KDIMGSENSOR_INVOKE_DRIVER_0] = (SensorEnum << KDIMGSENSOR_DUAL_SHIFT) | i;LOG_MSG("set sensor driver id =%x\n", id[KDIMGSENSOR_INVOKE_DRIVER_0]);//通过ioctl初始化camera sensor驱动err = ioctl(m_fdSensor, KDIMGSENSORIOC_X_SET_DRIVER,&id[KDIMGSENSOR_INVOKE_DRIVER_0] );if (err < 0) {LOG_ERR("ERROR:KDCAMERAHWIOC_X_SET_DRIVER\n");}//通过ioctl去检测camera sensor是否有效//err = open();err = ioctl(m_fdSensor, KDIMGSENSORIOC_T_CHECK_IS_ALIVE);if (err < 0) {LOG_MSG("[impSearchSensor] Err-ctrlCode (%s) \n", strerror(errno));}}
......
}

三：内核driver层

１．利用cmd命令KDIMGSENSORIOC_X_SET_DRIVER通过ioctl初始化sensor驱动，

//hal层的代码调用
kernel-3.18/drivers/misc/mediatek/imgsensor/src/mt3561/kd_sensorlist.cerr = ioctl(m_fdSensor, KDIMGSENSORIOC_X_SET_DRIVER,&id[KDIMGSENSOR_INVOKE_DRIVER_0] );

static long CAMERA_HW_Ioctl(struct file *a_pstFile,unsigned int a_u4Command, unsigned long a_u4Param)
{pIdx = (u32 *) pBuff;switch (a_u4Command) {case KDIMGSENSORIOC_X_SET_DRIVER:i4RetValue = kdSetDriver((unsigned int *)pBuff);}
}

int kdSetDriver(unsigned int *pDrvIndex)
{......//(1)初始化pSensorList指针，指向sensor驱动数组ACDK_KD_SENSOR_INIT_FUNCTION_STRUCT     //kdSensorList[MAX_NUM_OF_SUPPORT_SENSOR+1] if (0 != kdGetSensorInitFuncList(&pSensorList)) {PK_ERR("ERROR:kdGetSensorInitFuncList()\n");return -EIO;}//(2)调用pSensorList指向的ACDK_KD_SENSOR_INIT_FUNCTION_STRUCT类型中的SensorInit进行初始化。
pSensorList[drvIdx[i]].SensorInit(&g_pInvokeSensorFunc[i]);
......
}

分两部讲，第一步就是(1)初始化pSensorList指针，指向sensor驱动数组ACDK_KD_SENSOR_INIT_FUNCTION_STRUCT kdSensorList[MAX_NUM_OF_SUPPORT_SENSOR+1] ，来看下实现具体过程

UINT32 kdGetSensorInitFuncList(ACDK_KD_SENSOR_INIT_FUNCTION_STRUCT **ppSensorList)
{if (NULL == ppSensorList) {PK_ERR("[kdGetSensorInitFuncList]ERROR: NULL ppSensorList\n");return 1;}*ppSensorList = &kdSensorList[0];//执行kdSensorList数组的标号０，也就是开始地址。return 0;
} /* kdGetSensorInitFuncList() */

可以看到传进来的参数指针指向了kdSensorList数组的标号０，也就是该数组的开始地址，kdSensorList的定义如下：

//path:kernel-3.18/drivers/misc/mediatek/imgsensor/inc/kd_imgsensor_define.h
ACDK_KD_SENSOR_INIT_FUNCTION_STRUCT的声明：
typedef struct {MUINT32 SensorId;MUINT8 drvname[32];MUINT32(*SensorInit)(PSENSOR_FUNCTION_STRUCT *pfFunc);
} ACDK_KD_SENSOR_INIT_FUNCTION_STRUCT, *PACDK_KD_SENSOR_INIT_FUNCTION_STRUCT;//path:kernel-3.18/drivers/misc/mediatek/imgsensor/src/mt3561m/kd_sensorlist.h
ACDK_KD_SENSOR_INIT_FUNCTION_STRUCT kdSensorList[MAX_NUM_OF_SUPPORT_SENSOR+1] =
{#if defined(OV8825_MIPI_RAW){OV8825_SENSOR_ID, SENSOR_DRVNAME_OV8825_MIPI_RAW, OV8825_MIPI_RAW_SensorInit},
#endif
......
#if defined(RN6752_YUV){RN6752_SENSOR_ID, SENSOR_DRVNAME_RN6752_YUV, RN6752_YUV_SensorInit},
#endif
......
/*  ADD sensor driver before this line */{0,{0},NULL}, //end of list
};

可以看出kdSensorList是各个sensor型号驱动初始化结构体的数组。例如上面支持的RN6752_YUV型号的sensor驱动的初始化函数RN6752_YUV_SensorInit。

//RN6752_YUV　sensor驱动的操作集合
SENSOR_FUNCTION_STRUCT SensorFuncRN6752 =
{RN6752Open,RN6752GetInfo,RN6752GetResolution,RN6752FeatureControl,RN6752Control,RN6752Close,RN6752_Get_SignalStatus
};
//RN6752_YUV　sensor 驱动初始化
UINT32 RN6752_YUV_SensorInit(PSENSOR_FUNCTION_STRUCT *pfFunc)
{/* To Do: check sensor status here *///LOG_INF("Sensor init enter\n");if (pfFunc != NULL)*pfFunc = &SensorFuncRN6752;return ERROR_NONE;
} /* SensorInit() */

(2)上面第一步对pSensorList赋值后，接下来就可以调用sensor驱动的初始化获取sensor驱动的操作集合，如下：

pSensorList[drvIdx[i]].SensorInit(&g_pInvokeSensorFunc[i]);

最终便会执行到上面kdSensorList数组里面对应初始化函数，例如RN6752_YUV型号的sensor驱动的初始化函数RN6752_YUV_SensorInit，从下面初始化函数的逻辑得出执行完初始化函数后参数g_pInvokeSensorFunc数组中将会储存者RN6752_YUV型号的sensor驱动操作集合SensorFuncRN6752的地址。记住g_pInvokeSensorFunc这个变量后面会用到。

UINT32 RN6752_YUV_SensorInit(PSENSOR_FUNCTION_STRUCT *pfFunc)
{/* To Do: check sensor status here *///LOG_INF("Sensor init enter\n");if (pfFunc != NULL)*pfFunc = &SensorFuncRN6752;return ERROR_NONE;
} /* SensorInit() */

2.利用KDIMGSENSORIOC_T_CHECK_IS_ALIVE命令通过ioctl来获取sensor id值。

上面说完了sensor驱动的初始化完后，将会调用KDIMGSENSORIOC_T_CHECK_IS_ALIVE命令通过ioctl来检测sensor id的值。

err = ioctl(m_fdSensor, KDIMGSENSORIOC_T_CHECK_IS_ALIVE);

驱动层代码如下：

case KDIMGSENSORIOC_T_CHECK_IS_ALIVE:i4RetValue = adopt_CAMERA_HW_CheckIsAlive();

static inline int adopt_CAMERA_HW_CheckIsAlive(void)
{......if (g_pSensorFunc) {for (i = KDIMGSENSOR_INVOKE_DRIVER_0; i < KDIMGSENSOR_MAX_INVOKE_DRIVERS; i++) {if (DUAL_CAMERA_NONE_SENSOR != g_invokeSocketIdx[i]) {//次数通过sensorID变量获取sensor id的值err = g_pSensorFunc->SensorFeatureControl(g_invokeSocketIdx[i], SENSOR_FEATURE_CHECK_SENSOR_ID, (MUINT8 *)&sensorID, &retLen);if (sensorID == 0) {    /* not implement this feature ID */PK_DBG(" Not implement!!, use old open function to check\n");err = ERROR_SENSOR_CONNECT_FAIL;} else if (sensorID == 0xFFFFFFFF) {  /* fail to open the sensor */PK_DBG(" No Sensor Found");err = ERROR_SENSOR_CONNECT_FAIL;} else {PK_INF(" Sensor found ID = 0x%x\n", sensorID);snprintf(mtk_ccm_name, sizeof(mtk_ccm_name), "%s CAM[%d]:%s;", mtk_ccm_name, g_invokeSocketIdx[i], g_invokeSensorNameStr[i]);err = ERROR_NONE;}if (ERROR_NONE != err) {PK_DBG("ERROR:adopt_CAMERA_HW_CheckIsAlive(), No imgsensor alive\n");}}}}
......
}

上面主要通过
err = g_pSensorFunc->SensorFeatureControl(g_invokeSocketIdx[i], SENSOR_FEATURE_CHECK_SENSOR_ID, (MUINT8 *)&sensorID, &retLen);获取sensor id的值，查找g_pSensorFunc的定义赋值如下：

//path:kernel-3.18/drivers/misc/mediatek/imgsensor/src/mt3561/kd_sensorlist.c
static MULTI_SENSOR_FUNCTION_STRUCT2 *g_pSensorFunc = &kd_MultiSensorFunc;
MULTI_SENSOR_FUNCTION_STRUCT2  kd_MultiSensorFunc = {kd_MultiSensorOpen,kd_MultiSensorGetInfo,kd_MultiSensorGetResolution,kd_MultiSensorFeatureControl,kd_MultiSensorControl,kd_MultiSensorClose
};
//MULTI_SENSOR_FUNCTION_STRUCT2的类型声明
//path:kernel-3.18/drivers/misc/mediatek/imgsensor/inc/kd_imgsensor_define.h
typedef struct {MUINT32(*SensorOpen)(void);MUINT32(*SensorGetInfo)(MUINT32 *pScenarioId[2], MSDK_SENSOR_INFO_STRUCT * pSensorInfo[2], MSDK_SENSOR_CONFIG_STRUCT *pSensorConfigData[2]);MUINT32(*SensorGetResolution)(MSDK_SENSOR_RESOLUTION_INFO_STRUCT * pSensorResolution[2]);MUINT32(*SensorFeatureControl)(CAMERA_DUAL_CAMERA_SENSOR_ENUM InvokeCamera, MSDK_SENSOR_FEATURE_ENUM FeatureId, MUINT8 *pFeaturePara, MUINT32 *pFeatureParaLen);MUINT32(*SensorControl)(CAMERA_DUAL_CAMERA_SENSOR_ENUM InvokeCamera, MSDK_SCENARIO_ID_ENUM ScenarioId, MSDK_SENSOR_EXPOSURE_WINDOW_STRUCT *pImageWindow, MSDK_SENSOR_CONFIG_STRUCT *pSensorConfigData);MUINT32(*SensorClose)(void);
} MULTI_SENSOR_FUNCTION_STRUCT2, *PMULTI_SENSOR_FUNCTION_STRUCT2;

从上面可以的得知g_pSensorFunc->SensorFeatureControl调用的是kd_MultiSensorFeatureControl函数。kd_MultiSensorFeatureControl定义如下：

MUINT32
kd_MultiSensorFeatureControl(CAMERA_DUAL_CAMERA_SENSOR_ENUM InvokeCamera,MSDK_SENSOR_FEATURE_ENUM FeatureId,MUINT8 *pFeaturePara,MUINT32 *pFeatureParaLen)
{MUINT32 ret = ERROR_NONE;u32 i = 0;KD_MULTI_FUNCTION_ENTRY();for (i = KDIMGSENSOR_INVOKE_DRIVER_0; i < KDIMGSENSOR_MAX_INVOKE_DRIVERS; i++) {if (g_bEnableDriver[i] && g_pInvokeSensorFunc[i]) {if (InvokeCamera == g_invokeSocketIdx[i]) {.....//这里是主要的调用，获取sensor id值ret = g_pInvokeSensorFunc[i]->SensorFeatureControl(FeatureId, pFeaturePara, pFeatureParaLen);if (ERROR_NONE != ret) {PK_ERR("[%s]\n", __func__);return ret;}}}}KD_MULTI_FUNCTION_EXIT();return ERROR_NONE;
}

上面可以看出主要是通过ret = g_pInvokeSensorFunc[i]->SensorFeatureControl(FeatureId, pFeaturePara, pFeatureParaLen);来获取sensor id值，注意g_pInvokeSensorFunc这个指针是不是很熟悉，没错就是前面我们初始化sensor驱动的时候那个指针，所以这里调用 g_pInvokeSensorFunc[i]->SensorFeatureControl其实调用了具体的sensor型号的操作结合里面的SensorFeatureControl。上面我们所说的RN6752_YUV型号的sensor,那么这里调用的是RN6752FeatureControl。

//RN6752_YUV　sensor驱动的操作集合
SENSOR_FUNCTION_STRUCT SensorFuncRN6752 =
{RN6752Open,RN6752GetInfo,RN6752GetResolution,RN6752FeatureControl,RN6752Control,RN6752Close,RN6752_Get_SignalStatus
};

具体代码如下：这里在获取sensor id的时候传进来的FeatureId是SENSOR_FEATURE_CHECK_SENSOR_ID，因此会调用到RN6752GetSensorId(pFeatureData32)。

UINT32 RN6752FeatureControl(MSDK_SENSOR_FEATURE_ENUM FeatureId,UINT8 *pFeaturePara,UINT32 *pFeatureParaLen)
{UINT16 *pFeatureReturnPara16 = (UINT16 *) pFeaturePara;UINT16 *pFeatureData16 = (UINT16 *) pFeaturePara;UINT32 *pFeatureReturnPara32 = (UINT32 *) pFeaturePara;UINT32 *pFeatureData32 = (UINT32 *) pFeaturePara;//unsigned long long **pp64FeaturePara = (unsigned long long **)pFeaturePara;MSDK_SENSOR_CONFIG_STRUCT *pSensorConfigData = (MSDK_SENSOR_CONFIG_STRUCT *) pFeaturePara;MSDK_SENSOR_REG_INFO_STRUCT *pSensorRegData = (MSDK_SENSOR_REG_INFO_STRUCT *) pFeaturePara;switch (FeatureId) {case SENSOR_FEATURE_GET_RESOLUTION:*pFeatureReturnPara16++ = input_source_width;*pFeatureReturnPara16 = input_source_height;*pFeatureParaLen = 4;break;case SENSOR_FEATURE_GET_PERIOD:*pFeatureReturnPara16++ = input_source_width;*pFeatureReturnPara16 = input_source_height;*pFeatureParaLen = 4;break;case SENSOR_FEATURE_GET_PIXEL_CLOCK_FREQ:*pFeatureReturnPara32 = 27000000;*pFeatureParaLen = 4;break;case SENSOR_FEATURE_SET_ESHUTTER:break;case SENSOR_FEATURE_SET_NIGHTMODE:RN6752NightMode((BOOL) *pFeatureData16);break;case SENSOR_FEATURE_SET_GAIN:break;case SENSOR_FEATURE_SET_FLASHLIGHT:break;case SENSOR_FEATURE_SET_ISP_MASTER_CLOCK_FREQ:RN6752_isp_master_clock = *pFeatureData32;break;case SENSOR_FEATURE_SET_REGISTER:RN6752_write_cmos_sensor(pSensorRegData->RegAddr, pSensorRegData->RegData);break;case SENSOR_FEATURE_GET_REGISTER:pSensorRegData->RegData = RN6752_read_cmos_sensor(pSensorRegData->RegAddr);break;case SENSOR_FEATURE_GET_CONFIG_PARA:memcpy(pSensorConfigData, &RN6752SensorConfigData, sizeof(MSDK_SENSOR_CONFIG_STRUCT));*pFeatureParaLen = sizeof(MSDK_SENSOR_CONFIG_STRUCT);break;case SENSOR_FEATURE_SET_CCT_REGISTER:case SENSOR_FEATURE_SET_ENG_REGISTER:case SENSOR_FEATURE_GET_REGISTER_DEFAULT:case SENSOR_FEATURE_CAMERA_PARA_TO_SENSOR:case SENSOR_FEATURE_SENSOR_TO_CAMERA_PARA:case SENSOR_FEATURE_GET_GROUP_COUNT:*pFeatureReturnPara32++ = 0;*pFeatureParaLen = 4;break;case SENSOR_FEATURE_GET_GROUP_INFO:case SENSOR_FEATURE_GET_ITEM_INFO:case SENSOR_FEATURE_SET_ITEM_INFO:case SENSOR_FEATURE_GET_ENG_INFO:break;case SENSOR_FEATURE_GET_LENS_DRIVER_ID:// get the lens driver ID from EEPROM or just return LENS_DRIVER_ID_DO_NOT_CARE// if EEPROM does not exist in camera module.*pFeatureReturnPara32 = LENS_DRIVER_ID_DO_NOT_CARE;*pFeatureParaLen = 4;break;case SENSOR_FEATURE_SET_YUV_CMD:RN6752YUVSensorSetting((FEATURE_ID)*pFeatureData32, *(pFeatureData32+1));break;case SENSOR_FEATURE_SET_VIDEO_MODE:RN6752YUVSetVideoMode(*pFeatureData16);case SENSOR_FEATURE_CHECK_SENSOR_ID:RN6752GetSensorId(pFeatureData32);break;case SENSOR_FEATURE_GET_DELAY_INFO://LOG_INF("SENSOR_FEATURE_GET_DELAY_INFO\n");//RN6752YUVGetDelayInfo((uintptr_t)*pp64FeaturePara);break;case SENSOR_FEATURE_GET_INTERLACE_FLAG:if (source_format == PAL || source_format == NTSC){*pFeatureReturnPara32 = 1;} else {*pFeatureReturnPara32 = 0;}*pFeatureParaLen = 8;LOG_INF("*pFeatureReturnPara32: %d\n", *pFeatureReturnPara32);break;case SENSOR_FEATURE_SET_VIDEO_CHANNEL:RN6752_Set_Video_Channel(*pFeatureData16);LOG_INF("Richard *pFeatureData16: %d\n", *pFeatureData16);break;default:break;}return ERROR_NONE;
}

RN6752GetSensorId(pFeatureData32);的实现：

UINT32 RN6752GetSensorId(UINT32 *sensorId)
{int retry = 3;do {//获取sernsor id。主要是通过i2c获取0xfe寄存器的值与0xfd寄存器的值*sensorId = ((RN6752_read_cmos_sensor(0xfe) << 8) | RN6752_read_cmos_sensor(0xfd));LOG_ERR("WFH: sensor id = 0x%x", *sensorId);if (*sensorId == SENSOR_ID)break;retry--;} while (retry > 0);if (*sensorId != SENSOR_ID) {*sensorId = 0xFFFFFFFF;return ERROR_SENSOR_CONNECT_FAIL;}if (false == bRN6752_Inputsource_Format_Detected) {//RN6752ForceUpdateCVBSFormat();RN6752_PrestoreFormat();bRN6752_Inputsource_Format_Detected = true;}return ERROR_NONE;
}

也正是这里，因为获取sensor id的值失败，导致返回上层的camera个数为0，后来从log也能看出来，在进行i2c通信的时候出现i2c通信异常。